1. Field of the Invention
The present invention relates to a fire detector such as a flame detector and a smoke detector.
2. Description of the Related Art
A smoke detector is provided in a fire monitoring area such as a house or a building. A conventional smoke detector includes a first element substrate having a light-emitting element and a second element substrate having a light-receiving element, which are provided inside a casing (also referred to as an “optical case”). A main substrate including a power supply circuit, a current control circuit, an MPU, and the like is provided in a case. Electrical connection for transmission/reception of a signal and power feeding between the first and second element substrates and the main substrate is made through a signal line. The signal line connected to the first and second element substrates passes through a circular hole provided through a peripheral wall of the casing to extend along an outer surface of the peripheral wall so as to be connected to the main substrate (for example, see Japanese Patent Application Laid-open No. 2008-082708; hereinafter, referred to as Patent Document 1).
For inspecting and repairing the smoke detector described above, the first and second element substrates are required to be removed from and replaced into the casing. The signal line is introduced into the circular hole, and hence the signal line is required to be disconnected from the first and second element substrates so as to remove the first and second element substrates from the casing. Moreover, after the first and second element substrates are replaced in the casing, the first and second element substrates and the signal line are required to be connected to each other again. Much efforts are required to remove the element substrates from the casing and to replace the element substrates in the casing in the prior art as described above, and hence operating efficiency is lowered.
Further, in the conventional smoke detector described above, the signal line is provided from the hole formed through the peripheral wall of the casing to the main substrate without being shielded. Therefore, a noise component present inside the casing adversely affects an output of the signal line to result in malfunction of the smoke detector in some cases.